The production of high-purity hydrogen is of great interest industrially, the latter being widely used in many processes, such as hydrocracking, the production of methanol, the production of oxoalcohols and in isomerization processes.
In the prior art, PSA processes have proved to be very efficient in the separation of gas mixtures and in particular in the production of pure hydrogen or oxygen from gas mixtures contaminated by various impurities. PSA processes take advantage of the adsorption selectivity of a given adsorbent for one or a number of the contaminating substances of the gas mixture to be purified.
The choice of the adsorbent is problematic because it depends on the nature of the mixture to be treated. As a general rule, the adsorbents are selected according to their ability to adsorb and to desorb a specific compound. In fact, PSA processes involve the operation of pressure cycles. In a first phase, the adsorbent bed separates at least one constituent of the mixture by adsorption of this constituent on the adsorbent bed. In a second phase, the adsorbent is regenerated by lowering the pressure. At each new cycle, it is therefore essential for the desorption to be efficient and complete, so that there is an identical regenerated state at each new cycle. However, it is clear that this ability to adsorb and then desorb a specific constituent of a gas mixture is a function of the specific operating conditions of the PSA process envisaged and in particular of the temperature and pressure conditions.
However, insofar as the mixture to be purified generally comprises more than one impurity, it is desirable for the adsorbent to be able to adsorb and then desorb not one alone but a number of these impurities. In point of fact, the adsorption profile and selectivity for a given constituent are often influenced by the presence, in the gas mixture, of other impurities, this being due, for example, to possible competition or to poisoning of the adsorbent. These various considerations account for the complexity of the problem of the optimization of PSA processes by improvement of the adsorbent.